Method for removing initiators from grafting products

ABSTRACT

The present invention relates to a process for removing an initiator of cerium (IV) salt from a graft product. The process may include washing the graft product with a mineral acid solution comprising ascorbic acid.

The invention relates to an improved procedure for the removal ofinitiators from graft products, in which the grafting was initiated bymeans of cerium(IV) salts.

The grafting of unsaturated compounds onto basic supports containinghydroxyl groups, as is disclosed in DE 38 11 042 and DE 43 10 964 andthe publications EP 0 337 144 and EP 0 565 978 corresponding to these,is based on the procedure of Mino and Kaizermann (1958). Here, thegrafting is initiated by cerium(IV) salts.

Washing of the graft product with 0.5 M sulfuric acid, as well aswashing with acidic sodium sulfite solution (0.25 M solution of sodiumsulfite in 0.25 M sulfuric acid), is known for the removal of ceriumsalts from the graft product. This process, however, in many cases hasto be repeated a number of times in order to remove the cerium saltsadequately from the product. It is seen that for cation exchangers, e.g.graft polymers based on acrylamidomethylpropanesulfonic acid, thisprocedure is inadequate. Working with acidic sulfite solution isdisadvantageous for reasons of safety in the workplace. For other graftpolymers which, for example, contain epoxy groups, repeated washing withthe strong mineral acid is disadvantageous because a marked proportionof the epoxy groups are hydrolyzed here, or because the sulfite ionsreact with the epoxy groups. On account of this, in some graft products,in particular those which contain epoxy groups, a measurable residue(typically about 200 ppm of cerium) of cerium salts still remains in theproduct. In particular, if the separating materials prepared by means ofgrafting are used in biotechnology or for the preparation ofpharmaceutical products, removal of cerium salts to below the detectionlimit of atomic absorption spectroscopy (10 ppm) is an essentialproperty.

The object is thus to remove cerium salts from graft products which havebeen obtained by means of cerium(IV) initiation so that fewer than 100ppm of cerium remain in the product.

It has been found that cerium salts can be removed more completely fromthe graft products if a mineral acid solution of ascorbic acid is usedfor washing.

The invention relates to procedures for the removal of initiators fromgraft products, in which the grafting was initiated by means ofcerium(IV) salts, by washing with a mineral acid solution, ascorbic acidbeing added to this solution.

Apart from in the publications already mentioned, separating materialsbased on graft polymers in which the grafting is initiated usingcerium(IV) salts are disclosed in a number of further publications: EP 0697 905, EP 0 708 919, EP 0 721 372, EP 0 722 360, EP 0 722 361, EP 0722 362, EP 0 789 620 and PCT/EP 98/01 880.

According to the invention, the separating materials from which ceriumions are to be washed out are treated with a mineral acid solution ofascorbic acid; preferentially the concentration of ascorbic acid is 0.01to 2 mol/l, particularly preferably 0.1 to 0.5 mol/l, that of themineral acid 0.01 to 2 mol/l, particularly preferably 0.1 to 0.5 mol/l.Preferred mineral acids are perchloric acid and in particular sulfuricacid. The washing process is typically carried out at 4° C. to 80° C.,preferentially at 15° C. to 30° C., according to customary procedures,for example using a suction filter or by sedimentation and decantation.Washing is typically carried out with 3 to 10, usually 4 to 5, bedvolumes of the solution.

The concentrations of the cerium salts are determined by means ofoptical emission spectrometry using a commercially available ICPspectrometer. The proportion by weight of cerium is measured on thebasis of the calibration using cerium salts and customarily indicated inppm (parts per million) as the percentage by weight of cerium based onthe weight of the dried separating material. The separating material isdried for the analysis according to customary procedures, such that ithas a water content determined according to Karl-Fischer of less than0.1 percent by weight. Details of the cerium determination are found inExample 1. Using the process according to the invention, separatingmaterials are obtained which contain between 1 and 10 ppm, customarilybelow 1 ppm, of cerium.

Even without further details, it is to be assumed that a person skilledin the art can utilize the above description to the widest possibleextent. The preferred embodiments and examples are therefore only to beinterpreted as descriptive, but in no way as limiting disclosure in anymanner.

The complete disclosure of all applications, patents and publicationsmentioned above and below, in particular that of the correspondingapplication DE 198 37 020.2, filed on Aug. 14, 1998, are inserted intothis application by way of reference.

EXAMPLES Example 1

100 ml of a graft polymer based on Fractogel®, (Merck KGaA, Darmstadt,DE) containing 2-acrylamido-2-methylpropanesulfonic acid as monomerunits, prepared according to EP 0 337 144, are washed on a suctionfilter with four bed volumes of a solution of 0.2 M ascorbic acid in0.25 M sulfuric acid.

An aliquot (about 5-10 g) of the separating material is dried until thewater content according to Karl-Fischer is less than 0.1% by weight. Theweight of the dried separating material is then determined. Theseparating material is transferred to a 100 ml beaker and heated with 20ml of a mixture (1:1) of HNO₃ (65% by weight; item no. 441, Merck KGaA,DE) and H₂SO₄ (96% by weight; item no. 714, Merck KGaA, DE). H₂O₂ (30%by weight; p.a.; item no. 7209, Merck KGaA, DE) is added dropwise in thepresence of heat until the suspension is decolorized. After cooling toroom temperature (15-30° C.), the suspension is made up to 25 ml withwater. For the calibration solution, 0.5 ml of a cerium standardsolution (1 g/l; item no. 2612; Merck KGaA, DE) is treated with 20 ml ofthe above mixture of HNO₃ and H₂SO₄ as described for the solution to bemeasured and made up to 25 ml. A mixture consisting of 20 ml of NHO₃ andH₂SO₄, which is made up to 25 ml with water, is used as the blank value.

The ICP measurement is carried out in the following way:

Apparatus: Perkin-Elmer Optima 3000 DV;

Atomizer: Cross Flow;

Sample introduction: 1 ml/min;

Plasma power: 1500 Watt;

Plasma gas: 15 l/min;

Auxiliary gas: 0.5 l/min;

Atomizer gas: 0.75 l/min;

Observation mode: axial;

Emission line: 413.755 nm.

The concentration measured for the solution to be measured is convertedto the weight ratio ppm with the aid of the initial weight of thesample. The detection limit of the method is 10 ppm of cerium.

The content of cerium salts measured by means of atomic absorptionspectrometry is below the detection limit (10 ppm of cerium).

Example 2

100 ml of graft polymer containing epoxy groups and based on Fractogel®,prepared according to EP 0 565 978, are washed on a suction filter usingfour bed volumes of a solution of 0.25 M ascorbic acid in 0.25 Msulfuric acid.

The content of cerium salts measured by means of atomic absorptionspectrometry is below the detection limit (10 ppm).

Comparison Example

100 ml of graft polymer containing epoxy groups and based on Fractogel®,prepared according to EP 0 565 978, are washed on a suction filter withten bed volumes of 0.5 M sulfuric acid.

The content of cerium salts measured by means of atomic absorptionspectrometry is 237 ppm.

What is claimed is:
 1. A process for the removing an initiator of cerium(IV) salt from a graft product, comprising washing the graft productwith a mineral acid solution comprising ascorbic acid.
 2. A processaccording to claim 1, wherein the concentration of the ascorbic acid inthe solution is 0.01-2 mol/l.
 3. A process according to claim 1, whereinthe concentration of the ascorbic acid in the solution is 0.1-0.5 mol/l.4. A process according to claim 1, wherein the concentration of themineral acid in the mineral acid solution is 0.01-2 mol/l.
 5. A processaccording to claim 1, wherein the concentration of the mineral acid inthe mineral acid solution is 0.1-0.5 mol/l.
 6. A process according toclaim 2, wherein the concentration of the mineral acid in the mineralacid solution is 0.01-2 mol/l.
 7. A process according to claim 2,wherein the concentration of the mineral acid in the mineral acidsolution is 0.1-0.5 mol/l.
 8. A process according to claim 3, whereinthe concentration of the mineral acid in the mineral acid solution is0.01-2 mol/l.
 9. A process according to claim 3, wherein theconcentration of the mineral acid in the mineral acid solution is0.1-0.5 mol/l.
 10. A process according to claim 1, wherein said mineralacid solution comprises perchloric acid as a mineral acid.
 11. A processaccording to claim 1, wherein said mineral acid solution comprisessulfuric acid as a mineral acid.
 12. A process according to claim 1,wherein the washing is carried out at 4° C.-80° C.
 13. A processaccording to claim 1, wherein the washing is carried out at 15° C.-30°C.
 14. A process according to claim 1, wherein the washing is carriedout with 3 to 10 bed volumes of solution.
 15. A process according toclaim 1, wherein the washing is carried out with 4 to 5 bed volumes ofsolution.
 16. A process according to claim 1, wherein the graft productafter washing has less than 1 ppm of cerium.
 17. A process according toclaim 1, wherein the graft product after washing has less than 10 ppm ofcerium.
 18. A process according to claim 1, wherein the graft product tobe washed is obtained by grafting unsaturated compounds onto basicsupports wherein grafting is initiated by cerium (IV) salt.